In the case of a spindle head without a rotation lock (see, for example, German 39 30 121 C1), the spindle cannot be coupled by means of a simple form-locking coupling with the drive shaft. The spindle can also move into rotary settings in which the coupling elements are not aligned with one another, as is required for coupling.
With known spindle heads of the aforementioned type, one end of the bushing has a radially outwardly projecting annular flange. The flange has either a bolt extending in an axial direction or a catch with limiting surfaces extending in an axial direction, serving as the securing element. The housing is provided with a borehole or groove to receive the bolt or catch. Thus, the spindle retains the predetermined rotary setting taken upon uncoupling of the spindle from the drive shaft. This construction not only allows for a problem-free coupling, but also is often an indispensable condition for automatic replacement of the spindle head.
However, with these known spindle heads, the rotation lock can be misused as a counterhold element during tightening or as a chuck for the tool to be connected with the spindle, to avoid attaching a key or spanner to the spindle and using this key or spanner as a counterhold element during the tightening down movement. As a result of such misuse of the rotation lock, the bolt or catch can be broken off or damaged, such that the spindle can no longer be aligned properly with the housing.